RADIOSTEREOMETRY OF HIP PROSTHESES - REVIEW OF METHODOLOGY AND CLINICAL-RESULTS

Radiostereometric analysis is a science that enables reliable measurem ents to be made from radiographs. The method involves several steps in cluding insertion of spheric tantalum markers, radiographic examinatio ns, measurements of radiographic films, and calculations of three-dime nsional movements, The precision of the method corresponding to the 99 % significance interval varies between 0.15 and 0.6 mm and 0.3 degrees and 2 degrees when applied to total hip replacement depending on the technique used, Measurements of implant micromovement during 1 to 2 ye ars after surgery have proved to be of value to predict later clinical failure because of aseptic loosening and revision, Subsidence of the femoral stem or proximal migration of the acetabular cup between 1 and 2 mm has indicated increased risk of early or intermediate term revis ions in those prosthetic designs studied so far, Minimum early migrati on has been recorded for clinically well documented non-polished stems and polyethylene cups, which probably is one explanation for their lo ng term success. This small amount of early micromotion also has been found in porous coated and screw fixated press fit cups and all hydrox yapatite coated designs hitherto studied, As a first step in a clinica l evaluation of new implants or surgical techniques, the predictive va lue of radiostereometric analysis measurements can be used to reduce t he number of patients exposed to the potential risk of clinical failur e.